Implement scroll handler latency tracking

cc/trees/layer_tree_host.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/layer_tree_host.h"
 
 #include <algorithm>
 #include <stack>
 #include <string>
 
 #include "base/atomic_sequence_num.h"
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
 #include "base/message_loop/message_loop.h"
 #include "base/metrics/histogram.h"
 #include "base/stl_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "cc/animation/animation_registrar.h"
 #include "cc/animation/layer_animation_controller.h"
+#include "cc/base/latency_info_swap_promise.h"
 #include "cc/base/math_util.h"
 #include "cc/debug/devtools_instrumentation.h"
 #include "cc/debug/rendering_stats_instrumentation.h"
 #include "cc/input/layer_selection_bound.h"
 #include "cc/input/top_controls_manager.h"
 #include "cc/layers/heads_up_display_layer.h"
 #include "cc/layers/heads_up_display_layer_impl.h"
 #include "cc/layers/layer.h"
 #include "cc/layers/layer_iterator.h"
 #include "cc/layers/painted_scrollbar_layer.h"
@@ skipping 979 matching lines @@
       content_is_suitable_for_gpu_rasterization_ &=
           it->IsSuitableForGpuRasterization();
     }
 
     occlusion_tracker.LeaveLayer(it);
   }
 
   in_paint_layer_contents_ = false;
 }
 
-void LayerTreeHost::ApplyScrollAndScale(const ScrollAndScaleSet& info) {
+void LayerTreeHost::ApplyScrollAndScale(ScrollAndScaleSet* info) {
   if (!root_layer_.get())
     return;
 
+  ScopedPtrVector<LatencyInfoSwapPromise>::iterator it =
+      info->swap_promises.begin();
+  for (; it != info->swap_promises.end(); ++it) {
+    scoped_ptr<LatencyInfoSwapPromise> swap_promise(
+        info->swap_promises.take(it));
+    TRACE_EVENT_FLOW_STEP0(
+        "input",
+        "LatencyInfo.Flow",
+        TRACE_ID_DONT_MANGLE(swap_promise->latency_info().trace_id),

[danakj, 2014/07/09 15:50:35]

LGTM but if you were to put a TraceId() accessor on SwapPromise, then you could
keep all this general and not need to use the LatencyInfoSwapPromise type
anywhere in LTH/LTHI which might come in handy if we have another SwapPromise
type in the future.

+        "Main thread scroll update");
+    QueueSwapPromise(swap_promise.PassAs<SwapPromise>());
+  }
+
   gfx::Vector2d inner_viewport_scroll_delta;
   gfx::Vector2d outer_viewport_scroll_delta;
 
-  for (size_t i = 0; i < info.scrolls.size(); ++i) {
-    Layer* layer =
-        LayerTreeHostCommon::FindLayerInSubtree(root_layer_.get(),
-                                                info.scrolls[i].layer_id);
+  for (size_t i = 0; i < info->scrolls.size(); ++i) {
+    Layer* layer = LayerTreeHostCommon::FindLayerInSubtree(
+        root_layer_.get(), info->scrolls[i].layer_id);
     if (!layer)
       continue;
     if (layer == outer_viewport_scroll_layer_.get()) {
-      outer_viewport_scroll_delta += info.scrolls[i].scroll_delta;
+      outer_viewport_scroll_delta += info->scrolls[i].scroll_delta;
     } else if (layer == inner_viewport_scroll_layer_.get()) {
-      inner_viewport_scroll_delta += info.scrolls[i].scroll_delta;
+      inner_viewport_scroll_delta += info->scrolls[i].scroll_delta;
     } else {
       layer->SetScrollOffsetFromImplSide(layer->scroll_offset() +
-                                         info.scrolls[i].scroll_delta);
+                                         info->scrolls[i].scroll_delta);
     }
   }
 
   if (!inner_viewport_scroll_delta.IsZero() ||
-      !outer_viewport_scroll_delta.IsZero() || info.page_scale_delta != 1.f) {
+      !outer_viewport_scroll_delta.IsZero() || info->page_scale_delta != 1.f) {
     // SetScrollOffsetFromImplSide above could have destroyed the tree,
     // so re-get this layer before doing anything to it.
 
     // Preemptively apply the scroll offset and scale delta here before sending
     // it to the client.  If the client comes back and sets it to the same
     // value, then the layer can early out without needing a full commit.
     DCHECK(inner_viewport_scroll_layer_);  // We should always have this.
 
     inner_viewport_scroll_layer_->SetScrollOffsetFromImplSide(
         inner_viewport_scroll_layer_->scroll_offset() +
         inner_viewport_scroll_delta);
     if (outer_viewport_scroll_layer_) {
       outer_viewport_scroll_layer_->SetScrollOffsetFromImplSide(
           outer_viewport_scroll_layer_->scroll_offset() +
           outer_viewport_scroll_delta);
     }
-    ApplyPageScaleDeltaFromImplSide(info.page_scale_delta);
+    ApplyPageScaleDeltaFromImplSide(info->page_scale_delta);
 
     client_->ApplyScrollAndScale(
         inner_viewport_scroll_delta + outer_viewport_scroll_delta,
-        info.page_scale_delta);
+        info->page_scale_delta);
   }
 }
 
 void LayerTreeHost::StartRateLimiter() {
   if (animating_)
     return;
 
   if (!rate_limit_timer_.IsRunning()) {
     rate_limit_timer_.Start(FROM_HERE,
                             base::TimeDelta(),
@@ skipping 196 matching lines @@
   swap_promise_list_.push_back(swap_promise.Pass());
 }
 
 void LayerTreeHost::BreakSwapPromises(SwapPromise::DidNotSwapReason reason) {
   for (size_t i = 0; i < swap_promise_list_.size(); i++)
     swap_promise_list_[i]->DidNotSwap(reason);
   swap_promise_list_.clear();
 }
 
 }  // namespace cc